1. Field of the Invention
This invention relates to a device for the prevention of tooth decay and to a method of preventing tooth decay by use of such a device.
2. Prior Art
Prevention of tooth decay is important for good health and a variety of preventive methods have heretofore been used. But nevertheless, the rate of tooth decay is exceedingly high and, in particular, in the case of children the rate is as high as 90%. This fact indicates that it is difficult to impart perfect decay resistance to teeth by the conventional tooth decay prevention methods.
For clarity of description, the mechanical order of the development of a decayed tooth will now be described as follows: Generally, a region exposed above the tooth gum is called enamel, which consists chiefly of crystals of hydroxy apatite. The crystals abound in lattice defect and distortion. Also, the surface of the enamel appears very smooth to the naked eye, but it has been found through examination under an electronic scanning microscope, that the surface has tiny holes and side edges of deep-cut wavy stripes.
On the other hand, the inside of the mouth is a living place for various types of bacteria some of which function to dissolve sugar and produce lactic acid on the tooth surface. The lactic acid initially attacks the above-mentioned tiny holes and deep-cut peripheral side edges that exist inherently in the enamel and act on the hydroxy apatite, which is instable due to the lattice defect and distortion, and dissolves and decalcifies the hydroxy apatite and thereby destroys the enamel. This is the mechanical order in which teeth start to decay.
A description will now be given of the mechanical order of methods to prevent tooth decay heretofore in use. As is well known, the conventional methods are those in which fluorine was used. In these methods, a fluorine compound was brought into contact with the enamel of the teeth by the application of the fluorine compound to the teeth, whereby the fluorine ion (F-) is caused to act on the hydroxy apatite, which in turn, is changed into fluorapatite, which is resistant to acids and thereby prevents the decaying of the tooth enamel.
The conventional methods for preventing tooth decay described above is not free from disadvantages, which will now be discussed as follows: One of the disadvantages is that the above-mentioned methods are not always completely effective. As described above, in order to change hydroxy apatite into fluorapatite which is resistant to acids, a perfect reaction must be effected by bringing the fluorine ion (F-) sufficiently into contact with the crystal structures. But mere application of the fluorine compound to the enamel results in only a slight degree of formation of fluorapatite on the surface layer of the enamel with a strong possibility that the hydroxy apatite will not be fully fortified with a decay resistant property. Particularly, little or no fluorine ion (F-) goes into the enamel and no fluorapatite is produced at all. Accordingly, the remaining texture on the tooth surface is corroded by acids, melts and falls off to thereby bring a new hydroxy apatite texture into direct contact with acids, thus furthering the state of tooth decay, contrary to the original intention. It has been found in the present invention that the afore-mentioned tiny holes and peripheral side edges existing in the tooth enamel are a target area of tooth decay and that accordingly, as long as the tiny holes and side edges exist, no perfect result can be expected from the conventional tooth decay prevention methods in which fluorine is used. Another disadvantage inherent in the conventional methods is that these methods lack continuity in their effectiveness so that they need to have repeated applications of fluorine. This disadvantage, as previously pointed out, is due to the fact that it is difficult to create a sufficient chemical reaction from a single application of fluorine and that accordingly, a texture sufficient for effective prevention of tooth decay is apt to be lacking.
On the other hand, a method of irradiating giant pulses produced from Q-switched flash lamp excitation Nd:YAG laser upon the teeth is published by the present inventors and is widely known as a method which can eradicate the preceding drawbacks of conventional tooth decay prevention methods and impart effective decay-resistant properties to the tooth enamel by a single operation. The new method reveals that irradiation of giant pulses of energy density less than the order of 40 J/cm.sup.2 upon the teeth melts only a thin surface layer portion of the tooth enamel and thereby fills up the holes and peripheral wavy striped side edges existing on the tooth surface, thus eliminating the region subject to the initial attack of decay and increasing the decay-resistant properties of the teeth. The reason for the use of Nd:YAG laser as a laser oscillator is that the oscillation wavelength of this laser is 1.06 .mu.m and this wavelength acts selectively on the tooth enamel and does the least harm to the other regions. But the use of the Q-switched flash lamp excitation Nd:YAG laser in the context of the present invention provides serious disadvantages that will hereinafter be discussed. Namely, the flash lamp excitation laser is as low as several to a hundred pulses per second and because the average output of the laser is small notwithstanding the fact the the energy per giant pulse is great. Therefore, the effect of radiation per unit time becomes small and consequently, operation time per tooth becomes long. Also, because the giant pulses of the flash lamp excitation laser are exceedingly high in pulse peak output, normally several to some ten MW, there is a danger that the irradiation of the laser beams upon the teeth causes damage to the tooth surface. Furthermore, when flexible glass fibers are used in the guide for leading the laser beams from the oscillator to the region to be operated on luminous damage occurs and the fibers cannot be used but recourse must be made to the multi-joint manipulator or the like, with the result that adjustments and the operation become complicated.